In diapers, catamenial devices, and other absorbent devices, it is commonplace to have an absorbent material, for example, a batt made from cellulosic fluff, that is backed with a thin plastic film. The backing is supposed to retain moisture in the device. For comfort and additional moisture retention assurance, such devices have been designed to conform to the body. To make such a device conform to the body, an elastic member is often bonded to the plastic backing so as to create pleats or folds in the backing. The elastic is typically bonded to the flat backing while the elastic is stretched. After the elastic is secured, the elastic is released which causes the elastic to contract and gather the flat backing and the absorbent material into a curved shape that conforms to the body.
An example of a device and method of applying elastic to a flexible backing is illustrated in U.S. Pat. No. 4,397,704 issued to Frick on Aug. 9, 1983. This patent teaches that a flexible backing is corrugated by winding the backing onto a drum with corrugations formed in its circumference. While the drum is rotating, unstretched, adhesive-coated elastic strips are applied intermittently onto and perpendicular to the corrugations on the corrugated backing such that the elastic strips adhered only to the peaks, but not the valleys, of the corrugations. After the strips are adhered to the peaks, the flexible backing is unwound from the drum and stretched such that the corrugations are removed and the portions of the strips previously spanning the valleys contact the backing. The elastic is then adhered, along its length, to the stretched backing by passing the backing and elastic through nip rolls. When the assembly is allowed to relax after stretching, the elastic gathers the backing.
A problem with Frick's approach is that each piece of bonded elastic has regions of stretched and unstretched elastic between the ends of the elastic. Therefore, when the elastic strip is stretched to the extent that the flexible backing will permit, the unstretched regions correspond to those areas of the elastic that were originally adhered to the peaks of the corrugations in the unstretched state. The stretched regions correspond to those areas that spanned the valleys of the corrugations. The unstretched regions reduce the effectiveness of the elastic because they do not contribute to the gathering of the backing.
Such a situation can be tolerated in a large absorbent device such as a diaper. The elastic in a diaper is long enough that it can produce the desired curvature with much of the elastic effectively not utilized because it cannot be stretched.
The situation, however, cannot be tolerated in small absorbent devices such as catamenial devices where localized areas of the device have elastic bonded to it. A much larger percentage of stretchable elastic is needed per length of elastic in a small device to produce the body conformity desired.